m assumed by many
kinds, in the Flustra and others, in which the resemblance to sea-weeds
is so strong as generally to cause them to be confounded together under
the same group, and being fixed to submarine rocks, or marine shells,
observers might easily have been led to the mistake, had not modern
research rectified the error. Corals and Madrepores, as they are known
to us, consist but of the stony skeletons of the animals themselves, for
in the living state, while dwelling in the ocean, each portion of the
stony framework was covered with an animal coating of gelatinous matter,
which, closely investing it, was the living portion of the animal. But
the structure of the animal is not simply this, for attached to
different portions of it in the living state are to be found a countless
number of little cells, which, armed with tentacles of great prehensile
and tactile powers, are the apertures through which the particles of
food are conveyed for the sustenance of the animal These bodies as they
may be called, are the analogues of that simple polyp, the common hydra,
which, abounding in almost every pond, has been long known to
naturalists. It consists of a single dilated gelatinous vesicle, which
is terminated at one extremity by a sucker, and at the other by a number
of contractile filaments, which serve as the tentaculae, by which it
seizes its prey. This is all that represents the animal, the dilated
portion of the tube being the part in which the process of digestion is
carried on, and where the food is assimilated to the wants of the little
creature. These hydrae live singly, each animal being independent of
another, and each possesses the power of self-reparation; so that,
should it happen that a tentacle is lost, another sprouts to supply its
place, or should the naturalist by way of experiment divide it in half,
each portion immediately reproduces the wanting section. Such, then, is
briefly the structure of the simple fresh-water hydra, a polyp of common
occurrence, and from this description the reader will gain some idea of
the polyps of the Coral family before us; but he must remember that in
the case now under discussion, the polyps are aggregated together, a
number on one common stem, each possessing independent life, but all
ministering to the support of the compound animal.

The hydra, then, of the Coral and Madrepore, thus explained, would
appear to be the parts through which food is absorbed for the general